1. Field of the Invention
The disclosures herein generally relate to methods and apparatuses for forming images by use of electrostatic printing, and particularly relates to a method and apparatus for forming images in which color misalignment resulting from the positional misalignment of plural color developers disposed on a transfer body is corrected.
2. Description of the Related Art
Among various types of image forming apparatuses such as color copier machines and color laser printers, a tandem-type image forming apparatus transfers toner images corresponding to four developer colors, i.e., yellow., cyan, magenta, and black, successively onto a transfer body (e.g., transfer belt or transfer paper sheet). With such configuration, tandem-type image forming apparatuses tend to have a risk of developing color misalignment resulting from the mutual positional misalignment of toner images corresponding to respective colors. Such color misalignment greatly affects the quality of color images generated by fusing the toner images of respective colors onto a transfer paper sheet. It is thus a technical challenge to reduce color misalignment in such a type of image forming apparatus.
Japanese Patent Application Publication No. 2005-31227 (hereinafter referred to as Patent Document 1) discloses a positional misalignment correcting apparatus which optically detects a color-misalignment correction pattern comprised of several patches. The patches are formed on an intermediate transfer body by superimposing a reference color pattern and color patterns for correction (correction-purpose toner images) to correct the positional misalignment of each color based on the detected results. This position correcting apparatus includes a detecting means for detecting a specular reflection component and diffuse reflection component upon optically reading the misalignment correction pattern by use of a reflective-type photo sensor. The position correcting apparatus also includes a correction means for correcting positional misalignment based on the detected specular reflection component and diffuse reflection component. A glossiness of the intermediate transfer body is determined based on the specular reflection component detected upon optically reading the misalignment correction pattern by use of the reflective-type photo sensor. A luminance is determined based on the detected diffuse reflection component.
Japanese Patent Application Publication No. 2002-236402 (hereinafter referred to as Patent Document 2) discloses an image forming method that forms color toner reference images (i.e., correction-purpose toner images) on an image carrying member or transfer-object carrying member. The image forming method also detects reflective light from the reference images by use of both a diffuse-reflection-type detector and a specular-reflection-type detector. The image forming method then corrects the output value of the diffuse-reflection-type detector based on the output value of the specular-reflection-type detector and the output value of the diffuse-reflection-type detector.
In the technologies disclosed in Patent Document 1 and Patent Document 2, a correction-purpose toner image is detected by use of a light emission device and a detector that is provided with a light receiving device for receiving a specular reflection component and a light receiving device for receiving a diffuse reflection component. If a detector provided with a single light receiving device were able to be used, however, a cost reduction and size reduction of the detector could be achieved by detecting the correction-purpose toner image using the specular reflection component received by the single light receiving device.
If the above-noted detector is placed such that the optical axis of the light emitting device and the optical axis of the light receiving device cross each other on the surface of a transfer body within a plane parallel to the normal line of the transfer body, the reflective light received by the light receiving device will mostly be a specular reflection component, thereby being able to disregard the effect of a diffuse light component. If the optical axis of the light emitting device and the optical axis of the light receiving device are misaligned due to manufacturing variation of the detector, however, the effect of a diffuse reflection component contained in the reflective light received by the light receiving device cannot be disregarded, thereby degrading the detection accuracy of the detector.
What is needed is an image forming method and image forming apparatus that is implemented by use of an inexpensive configuration, yet can accurately detect a correction-purpose toner image.